Black Screen with Audio

I’m working on troubleshooting a 65” Sony tv model xbr-65x850f that was manufactured in 2018. The tv turns on/off but does not display any images (flashlight test) and I cannot see any backlight. There is audio. What is interesting is that when I perform a complete factory reset, I can see traces of picture with a flashlight, but when I turn off the TV and turn it back on, it’s gone. So far, I’ve checked the power supply unit output to the main board and t-con and the voltage readings are correct. I tried measuring the +out and -out voltages that I assume feed to the LED lights but I’m not too sure if what I’ve measured is correct. For all the +out pins, I was reading around 71V with the power on. I was getting 0v for the -out pins. The power supply board has text that says LED==117.4V. Could that be the issue? The power supply board model is AP-P288AM.

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I’m also trying to measure voltages on the t-con board but cannot find any test pads. Can I get some insight on how to measure the voltage for VCC, VDD, VGL, VGH, etc? The t-con board model is 6870c-0749a.

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@iamme57002 the voltage for the backlight would be to low. Make sure you measured correctly (not saying you didn't or questioning your skills. Just wanting to make sure) Hard to see on your image, but it looks like CN6401 connects to your main board. Post some clear, close up pictures of those areas (Legend and connector). Do you get all the voltages on there? What voltages do you get for BL_On?

As for the voltages on your T-con board. Manufacturers use a bunch of different designators i.e. VGL is also Voff/VGOFF/VEEG etc so it all depends on who makes the board. As you probably already found out, schematics are really hard to come by. There are some test points on your T-con, but they have the green masking of them. You need a small, sharp scalpel to remove the masking and test. For example, above R280 to the right of the large IC you can see VGL_2 in green. You would need to scrape the maskingaway. They are all getting wiser to us and do not want us to do our own repairs. Things are being made more complicated for the DIY'er.


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